The present invention relates to a non-aqueous electrolyte secondary battery, in which is used lithium or a substance capable of absorbing and desorbing lithium for the active material for the positive or negative electrode and which contains a lithium ion-conductive non-aqueous electrolyte, in particular, to improvements in the charge-discharge latitude in the battery.
Recent developments in a variety of portable electronic appliances and communication appliances are remarkable, and many of such appliances require high-power batteries. In that situation, there is a great demand for secondary batteries with increased energy density for economic, down-sized and lightweight appliances. For these, non-aqueous electrolyte secondary batteries with increased energy density have been being studied and developed, and some of them are now in practical use.
In ordinary secondary batteries of that type, LiCoO2, LiMnO2, Li4Mn5O12 or the like is used for the positive electrode active material, and lithium metal or a substance capable of absorbing and desorbing lithium, such as LiTi2O4, Li4Ti5O12 or the like, is for the negative electrode active material. Secondary batteries comprising a combination of these have the advantage of large charge-discharge capacity, but must be charged at high voltage of around 3 V or so in order that they could fully ensure their capacity.
Portable electronic appliances and communication appliances capable of being driven even at low voltage are desired these days, for which, therefore, desired are secondary batteries capable of fully ensuring their capabilities even when charged at low voltage of around 2.5 V or so.
In order to meet the recent charge requirements as above that differ from the conventional ones in the art, the present invention is to provide a positive or negative electrode active material capable of ensuring good charge-discharge characteristics even at voltage differing from that for conventional secondary batteries.
Using a composite oxide of a compositional formula, LiaCubTicO4 (in which 0 less than axe2x89xa61, 0 less than bxe2x89xa60.5, 1.5xe2x89xa6c less than 2) for the positive or negative electrode herein, the invention has made it possible to fabricate a non-aqueous electrolyte secondary battery capable of being charged at voltage differing from that for conventional batteries.